When efficiency of communication within a parallel computer is improved by optimizing a connection form between servers and switches (that is, network topology) in the parallel computer, it is possible to increase throughput of parallel distributed processing executed by the parallel computer. When it is possible to connect a large number of servers with a small number of switches by optimizing the network topology in the parallel computer, the construction cost of the parallel computer may be reduced.
A network topology called Latin square fat tree is known. The Latin square fat tree has a feature that there exists only one route via a Spine switch between any two different Leaf switches. When the Latin square fat tree is used, it is possible to connect more servers with the same number of switches as compared with a general two-stage fat tree.
Each Leaf switch in a system (hereafter, referred to as a Latin square fat tree system) employing the Latin square fat tree is connected to a plurality of servers and a plurality of Spine switches through a plurality of links. Accordingly, there are cases where a Leaf switch may be used for another collective communication when the Leaf switch is used for certain collective communication, but such a point of view is not paid attention to.
Related techniques are disclosed in, for example, M. Valerio, L. E. Moser and P. M. Melliar-Smith, “Recursively Scalable Fat-Trees as Interconnection Networks”, IEEE 13th Annual International Phoenix Conference on Computers and Communications, 1994.